Research On IQ Mismatch And Phase Noise Suppression Algorithm In Polarization Division Multiplexing Coherent Optical OFDM Systems

The technology of PDM CO-OFDM is very popular recent years in the filed of optical fiber communication,this technology not only possesses the advantages of the OFDM technology that has high tolerance of the CD and PMD,high spectrum efficiency and long transmission distance,but also gets the strengths of the PDM technology which can evidently increase the channel capability and transmission rate.However,the nonidealness of the devices would lead to the amplitude and phase imbalance of the in-phase and quadrature phase?IQ?signals in transmitter?Tx?and receiver?Rx?during coherent detection and IQ modulation,the linewidth of the Tx and Rx laser would cause the phase noise of the laser,both IQ balance and phase noise would degrade the performance.This paper mainly studies the IQ imbalance and phase noise suppression algorithm in PDM CO-OFDM system,the details are as follows:?1?A novel pilot structure for Tx IQ imbalance and phase noise suppression is proposed.Considering the existing researches haven't compensated the IQ imbalance and phase noise at the same time,this paper construct the new mathematic model and design the novel pilot structure including the block-types pilot and comb-type pilot that are used for IQ imbalance and phase noise compensation,respectively.Simulation results show that in 100Gb/s system through 560km transmission,while the phase imbalance is 15°,amplitude imbalance is 3dB and laser linewidth is 100kHz,the BER of the proposed method is from the level of10^-1to10^-2while the proposed method can achieve effective transmission at1?10^-3,meanwhile the complexity the proposed method reduces about 63%after comparison and analysis.?2?A novel scheme for Rx IQ imbalance and phase noise suppression is proposed.The compared method uses the GSOP algorithm and conventional training symbols to compensate the IQ imbalance and channel distortion.However,GSOP method is not able to suppress the IQ imbalance completely,and the channel distortion estimation would be affected by the residual IQ imbalance which would do harm to the system performance.This paper rededuce the mathematic model considering the phase noise and design a novel pilot structure combining with the GSOP method that can achieve the suppression of the channel distortion estimation errors brought by residual IQ imbalance as well as the compensation of the phase noise.Simulation results show that in 100Gb/s system through 480km transmission,while the phase imbalance is 10°,amplitude imbalance is 2dB and laser linewidth is 100kHz,when the BER is1?10^-3the OSNR punishment of the proposed method decreases about 6dB and the tolerance of the phase imbalance and amplitude imbalance increase about 14°and 3dB,respectively.